Light bulb having a heat sink



FIG. 1 is a perspective view of a light bulb having a heat sink showing my new design;

FIG. 2 is a front plan view thereof;

FIG. 3 is a side plan view thereof;

FIG. 4 is a top plan view thereof; and,

FIG. 5 is a bottom plan view thereof. 

The ornamental design for a light bulb having a heat sink, as shown and described. 